Memories, such as memory devices, may typically be provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory, including random-access memory (RAM), read only memory (ROM), dynamic random-access memory (DRAM), synchronous dynamic random-access memory (SDRAM), resistance variable memory, and flash memory, among others. Types of resistance variable memory may include phase-change-material (PCM) memory, programmable-conductor memory, and resistive random-access memory (RRAM), among others.
Memory devices may be utilized as volatile and non-volatile memory for a wide range of electronic applications in need of high memory densities, high reliability, and low power consumption. Non-volatile memory may be used in, for example, personal computers, portable memory sticks, solid state drives (SSDs), digital cameras, cellular telephones, portable music players such as MP3 players, and movie players, among other electronic devices.
Resistance variable memory devices can include resistive memory cells that can store data based on the resistance state of a storage element (e.g., a resistive memory element having a variable resistance). As such, resistive memory cells may be programmed to store data corresponding to a target data state by varying the resistance level of the resistive memory element. Resistive memory cells may be programmed to a target data state (e.g., corresponding to a particular resistance state) by applying sources of an electrical field or energy, such as positive or negative electrical pulses (e.g., positive or negative voltage or current pulses) to the cells (e.g., to the resistive memory element of the cells) for a particular duration. A state of a resistive memory cell may be determined by sensing current through the cell responsive to an applied interrogation voltage. The sensed current, which varies based on the resistance level of the cell, can indicate the state of the cell.
One of a number of data states (e.g., resistance states) may be set for a resistive memory cell. For example, a single level memory cell (SLC) may be programmed to a targeted one of two different data states, which may be represented by the binary units 1 or 0 and can depend on whether the cell is programmed to a resistance above or below a particular level. As an additional example, some resistive memory cells may be programmed to a targeted one of more than two data states (e.g., 1111, 0111, 0011, 1011, 1001, 0001, 0101, 1101, 1100, 0100, 0000, 1000, 1010, 0010, 0110, and 1110). Such cells may be referred to as multi state memory cells, multiunit cells, or multilevel cells (MLCs). MLCs can provide higher density memories without increasing the number of memory cells since each cell can represent more than one digit (e.g., more than one bit).